arch/tile/kernel/backtrace.c

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/string.h>
  17
  18 #include <asm/backtrace.h>
  19
  20 #include <arch/chip.h>
  21
  22 #if TILE_CHIP < 10
  23
  24
  25 #include <asm/opcode-tile.h>
  26
  27
  28 #define TREG_SP 54
  29 #define TREG_LR 55
  30
  31
  32 /** A decoded bundle used for backtracer analysis. */
  33 struct BacktraceBundle {
  34         tile_bundle_bits bits;
  35         int num_insns;
  36         struct tile_decoded_instruction
  37         insns[TILE_MAX_INSTRUCTIONS_PER_BUNDLE];
  38 };
  39
  40
  41 /* This implementation only makes sense for native tools. */
  42 /** Default function to read memory. */
  43 static bool bt_read_memory(void *result, VirtualAddress addr,
  44                            size_t size, void *extra)
  45 {
  46         /* FIXME: this should do some horrible signal stuff to catch
  47          * SEGV cleanly and fail.
  48          *
  49          * Or else the caller should do the setjmp for efficiency.
  50          */
  51
  52         memcpy(result, (const void *)addr, size);
  53         return true;
  54 }
  55
  56
  57 /** Locates an instruction inside the given bundle that
  58  * has the specified mnemonic, and whose first 'num_operands_to_match'
  59  * operands exactly match those in 'operand_values'.
  60  */
  61 static const struct tile_decoded_instruction *find_matching_insn(
  62         const struct BacktraceBundle *bundle,
  63         tile_mnemonic mnemonic,
  64         const int *operand_values,
  65         int num_operands_to_match)
  66 {
  67         int i, j;
  68         bool match;
  69
  70         for (i = 0; i < bundle->num_insns; i++) {
  71                 const struct tile_decoded_instruction *insn =
  72                         &bundle->insns[i];
  73
  74                 if (insn->opcode->mnemonic != mnemonic)
  75                         continue;
  76
  77                 match = true;
  78                 for (j = 0; j < num_operands_to_match; j++) {
  79                         if (operand_values[j] != insn->operand_values[j]) {
  80                                 match = false;
  81                                 break;
  82                         }
  83                 }
  84
  85                 if (match)
  86                         return insn;
  87         }
  88
  89         return NULL;
  90 }
  91
  92 /** Does this bundle contain an 'iret' instruction? */
  93 static inline bool bt_has_iret(const struct BacktraceBundle *bundle)
  94 {
  95         return find_matching_insn(bundle, TILE_OPC_IRET, NULL, 0) != NULL;
  96 }
  97
  98 /** Does this bundle contain an 'addi sp, sp, OFFSET' or
  99  * 'addli sp, sp, OFFSET' instruction, and if so, what is OFFSET?
 100  */
 101 static bool bt_has_addi_sp(const struct BacktraceBundle *bundle, int *adjust)
 102 {
 103         static const int vals[2] = { TREG_SP, TREG_SP };
 104
 105         const struct tile_decoded_instruction *insn =
 106                 find_matching_insn(bundle, TILE_OPC_ADDI, vals, 2);
 107         if (insn == NULL)
 108                 insn = find_matching_insn(bundle, TILE_OPC_ADDLI, vals, 2);
 109         if (insn == NULL)
 110                 return false;
 111
 112         *adjust = insn->operand_values[2];
 113         return true;
 114 }
 115
 116 /** Does this bundle contain any 'info OP' or 'infol OP'
 117  * instruction, and if so, what are their OP?  Note that OP is interpreted
 118  * as an unsigned value by this code since that's what the caller wants.
 119  * Returns the number of info ops found.
 120  */
 121 static int bt_get_info_ops(const struct BacktraceBundle *bundle,
 122                 int operands[MAX_INFO_OPS_PER_BUNDLE])
 123 {
 124         int num_ops = 0;
 125         int i;
 126
 127         for (i = 0; i < bundle->num_insns; i++) {
 128                 const struct tile_decoded_instruction *insn =
 129                         &bundle->insns[i];
 130
 131                 if (insn->opcode->mnemonic == TILE_OPC_INFO ||
 132                     insn->opcode->mnemonic == TILE_OPC_INFOL) {
 133                         operands[num_ops++] = insn->operand_values[0];
 134                 }
 135         }
 136
 137         return num_ops;
 138 }
 139
 140 /** Does this bundle contain a jrp instruction, and if so, to which
 141  * register is it jumping?
 142  */
 143 static bool bt_has_jrp(const struct BacktraceBundle *bundle, int *target_reg)
 144 {
 145         const struct tile_decoded_instruction *insn =
 146                 find_matching_insn(bundle, TILE_OPC_JRP, NULL, 0);
 147         if (insn == NULL)
 148                 return false;
 149
 150         *target_reg = insn->operand_values[0];
 151         return true;
 152 }
 153
 154 /** Does this bundle modify the specified register in any way? */
 155 static bool bt_modifies_reg(const struct BacktraceBundle *bundle, int reg)
 156 {
 157         int i, j;
 158         for (i = 0; i < bundle->num_insns; i++) {
 159                 const struct tile_decoded_instruction *insn =
 160                         &bundle->insns[i];
 161
 162                 if (insn->opcode->implicitly_written_register == reg)
 163                         return true;
 164
 165                 for (j = 0; j < insn->opcode->num_operands; j++)
 166                         if (insn->operands[j]->is_dest_reg &&
 167                             insn->operand_values[j] == reg)
 168                                 return true;
 169         }
 170
 171         return false;
 172 }
 173
 174 /** Does this bundle modify sp? */
 175 static inline bool bt_modifies_sp(const struct BacktraceBundle *bundle)
 176 {
 177         return bt_modifies_reg(bundle, TREG_SP);
 178 }
 179
 180 /** Does this bundle modify lr? */
 181 static inline bool bt_modifies_lr(const struct BacktraceBundle *bundle)
 182 {
 183         return bt_modifies_reg(bundle, TREG_LR);
 184 }
 185
 186 /** Does this bundle contain the instruction 'move fp, sp'? */
 187 static inline bool bt_has_move_r52_sp(const struct BacktraceBundle *bundle)
 188 {
 189         static const int vals[2] = { 52, TREG_SP };
 190         return find_matching_insn(bundle, TILE_OPC_MOVE, vals, 2) != NULL;
 191 }
 192
 193 /** Does this bundle contain the instruction 'sw sp, lr'? */
 194 static inline bool bt_has_sw_sp_lr(const struct BacktraceBundle *bundle)
 195 {
 196         static const int vals[2] = { TREG_SP, TREG_LR };
 197         return find_matching_insn(bundle, TILE_OPC_SW, vals, 2) != NULL;
 198 }
 199
 200 /** Locates the caller's PC and SP for a program starting at the
 201  * given address.
 202  */
 203 static void find_caller_pc_and_caller_sp(CallerLocation *location,
 204                                          const VirtualAddress start_pc,
 205                                          BacktraceMemoryReader read_memory_func,
 206                                          void *read_memory_func_extra)
 207 {
 208         /* Have we explicitly decided what the sp is,
 209          * rather than just the default?
 210          */
 211         bool sp_determined = false;
 212
 213         /* Has any bundle seen so far modified lr? */
 214         bool lr_modified = false;
 215
 216         /* Have we seen a move from sp to fp? */
 217         bool sp_moved_to_r52 = false;
 218
 219         /* Have we seen a terminating bundle? */
 220         bool seen_terminating_bundle = false;
 221
 222         /* Cut down on round-trip reading overhead by reading several
 223          * bundles at a time.
 224          */
 225         tile_bundle_bits prefetched_bundles[32];
 226         int num_bundles_prefetched = 0;
 227         int next_bundle = 0;
 228         VirtualAddress pc;
 229
 230         /* Default to assuming that the caller's sp is the current sp.
 231          * This is necessary to handle the case where we start backtracing
 232          * right at the end of the epilog.
 233          */
 234         location->sp_location = SP_LOC_OFFSET;
 235         location->sp_offset = 0;
 236
 237         /* Default to having no idea where the caller PC is. */
 238         location->pc_location = PC_LOC_UNKNOWN;
 239
 240         /* Don't even try if the PC is not aligned. */
 241         if (start_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0)
 242                 return;
 243
 244         for (pc = start_pc;; pc += sizeof(tile_bundle_bits)) {
 245
 246                 struct BacktraceBundle bundle;
 247                 int num_info_ops, info_operands[MAX_INFO_OPS_PER_BUNDLE];
 248                 int one_ago, jrp_reg;
 249                 bool has_jrp;
 250
 251                 if (next_bundle >= num_bundles_prefetched) {
 252                         /* Prefetch some bytes, but don't cross a page
 253                          * boundary since that might cause a read failure we
 254                          * don't care about if we only need the first few
 255                          * bytes. Note: we don't care what the actual page
 256                          * size is; using the minimum possible page size will
 257                          * prevent any problems.
 258                          */
 259                         unsigned int bytes_to_prefetch = 4096 - (pc & 4095);
 260                         if (bytes_to_prefetch > sizeof prefetched_bundles)
 261                                 bytes_to_prefetch = sizeof prefetched_bundles;
 262
 263                         if (!read_memory_func(prefetched_bundles, pc,
 264                                               bytes_to_prefetch,
 265                                               read_memory_func_extra)) {
 266                                 if (pc == start_pc) {
 267                                         /* The program probably called a bad
 268                                          * address, such as a NULL pointer.
 269                                          * So treat this as if we are at the
 270                                          * start of the function prolog so the
 271                                          * backtrace will show how we got here.
 272                                          */
 273                                         location->pc_location = PC_LOC_IN_LR;
 274                                         return;
 275                                 }
 276
 277                                 /* Unreadable address. Give up. */
 278                                 break;
 279                         }
 280
 281                         next_bundle = 0;
 282                         num_bundles_prefetched =
 283                                 bytes_to_prefetch / sizeof(tile_bundle_bits);
 284                 }
 285
 286                 /* Decode the next bundle. */
 287                 bundle.bits = prefetched_bundles[next_bundle++];
 288                 bundle.num_insns =
 289                         parse_insn_tile(bundle.bits, pc, bundle.insns);
 290                 num_info_ops = bt_get_info_ops(&bundle, info_operands);
 291
 292                 /* First look at any one_ago info ops if they are interesting,
 293                  * since they should shadow any non-one-ago info ops.
 294                  */
 295                 for (one_ago = (pc != start_pc) ? 1 : 0;
 296                      one_ago >= 0; one_ago--) {
 297                         int i;
 298                         for (i = 0; i < num_info_ops; i++) {
 299                                 int info_operand = info_operands[i];
 300                                 if (info_operand < CALLER_UNKNOWN_BASE) {
 301                                         /* Weird; reserved value, ignore it. */
 302                                         continue;
 303                                 }
 304
 305                                 /* Skip info ops which are not in the
 306                                  * "one_ago" mode we want right now.
 307                                  */
 308                                 if (((info_operand & ONE_BUNDLE_AGO_FLAG) != 0)
 309                                     != (one_ago != 0))
 310                                         continue;
 311
 312                                 /* Clear the flag to make later checking
 313                                  * easier. */
 314                                 info_operand &= ~ONE_BUNDLE_AGO_FLAG;
 315
 316                                 /* Default to looking at PC_IN_LR_FLAG. */
 317                                 if (info_operand & PC_IN_LR_FLAG)
 318                                         location->pc_location =
 319                                                 PC_LOC_IN_LR;
 320                                 else
 321                                         location->pc_location =
 322                                                 PC_LOC_ON_STACK;
 323
 324                                 switch (info_operand) {
 325                                 case CALLER_UNKNOWN_BASE:
 326                                         location->pc_location = PC_LOC_UNKNOWN;
 327                                         location->sp_location = SP_LOC_UNKNOWN;
 328                                         return;
 329
 330                                 case CALLER_SP_IN_R52_BASE:
 331                                 case CALLER_SP_IN_R52_BASE | PC_IN_LR_FLAG:
 332                                         location->sp_location = SP_LOC_IN_R52;
 333                                         return;
 334
 335                                 default:
 336                                 {
 337                                         const unsigned int val = info_operand
 338                                                 - CALLER_SP_OFFSET_BASE;
 339                                         const unsigned int sp_offset =
 340                                                 (val >> NUM_INFO_OP_FLAGS) * 8;
 341                                         if (sp_offset < 32768) {
 342                                                 /* This is a properly encoded
 343                                                  * SP offset. */
 344                                                 location->sp_location =
 345                                                         SP_LOC_OFFSET;
 346                                                 location->sp_offset =
 347                                                         sp_offset;
 348                                                 return;
 349                                         } else {
 350                                                 /* This looked like an SP
 351                                                  * offset, but it's outside
 352                                                  * the legal range, so this
 353                                                  * must be an unrecognized
 354                                                  * info operand.  Ignore it.
 355                                                  */
 356                                         }
 357                                 }
 358                                 break;
 359                                 }
 360                         }
 361                 }
 362
 363                 if (seen_terminating_bundle) {
 364                         /* We saw a terminating bundle during the previous
 365                          * iteration, so we were only looking for an info op.
 366                          */
 367                         break;
 368                 }
 369
 370                 if (bundle.bits == 0) {
 371                         /* Wacky terminating bundle. Stop looping, and hope
 372                          * we've already seen enough to find the caller.
 373                          */
 374                         break;
 375                 }
 376
 377                 /*
 378                  * Try to determine caller's SP.
 379                  */
 380
 381                 if (!sp_determined) {
 382                         int adjust;
 383                         if (bt_has_addi_sp(&bundle, &adjust)) {
 384                                 location->sp_location = SP_LOC_OFFSET;
 385
 386                                 if (adjust <= 0) {
 387                                         /* We are in prolog about to adjust
 388                                          * SP. */
 389                                         location->sp_offset = 0;
 390                                 } else {
 391                                         /* We are in epilog restoring SP. */
 392                                         location->sp_offset = adjust;
 393                                 }
 394
 395                                 sp_determined = true;
 396                         } else {
 397                                 if (bt_has_move_r52_sp(&bundle)) {
 398                                         /* Maybe in prolog, creating an
 399                                          * alloca-style frame.  But maybe in
 400                                          * the middle of a fixed-size frame
 401                                          * clobbering r52 with SP.
 402                                          */
 403                                         sp_moved_to_r52 = true;
 404                                 }
 405
 406                                 if (bt_modifies_sp(&bundle)) {
 407                                         if (sp_moved_to_r52) {
 408                                                 /* We saw SP get saved into
 409                                                  * r52 earlier (or now), which
 410                                                  * must have been in the
 411                                                  * prolog, so we now know that
 412                                                  * SP is still holding the
 413                                                  * caller's sp value.
 414                                                  */
 415                                                 location->sp_location =
 416                                                         SP_LOC_OFFSET;
 417                                                 location->sp_offset = 0;
 418                                         } else {
 419                                                 /* Someone must have saved
 420                                                  * aside the caller's SP value
 421                                                  * into r52, so r52 holds the
 422                                                  * current value.
 423                                                  */
 424                                                 location->sp_location =
 425                                                         SP_LOC_IN_R52;
 426                                         }
 427                                         sp_determined = true;
 428                                 }
 429                         }
 430                 }
 431
 432                 if (bt_has_iret(&bundle)) {
 433                         /* This is a terminating bundle. */
 434                         seen_terminating_bundle = true;
 435                         continue;
 436                 }
 437
 438                 /*
 439                  * Try to determine caller's PC.
 440                  */
 441
 442                 jrp_reg = -1;
 443                 has_jrp = bt_has_jrp(&bundle, &jrp_reg);
 444                 if (has_jrp)
 445                         seen_terminating_bundle = true;
 446
 447                 if (location->pc_location == PC_LOC_UNKNOWN) {
 448                         if (has_jrp) {
 449                                 if (jrp_reg == TREG_LR && !lr_modified) {
 450                                         /* Looks like a leaf function, or else
 451                                          * lr is already restored. */
 452                                         location->pc_location =
 453                                                 PC_LOC_IN_LR;
 454                                 } else {
 455                                         location->pc_location =
 456                                                 PC_LOC_ON_STACK;
 457                                 }
 458                         } else if (bt_has_sw_sp_lr(&bundle)) {
 459                                 /* In prolog, spilling initial lr to stack. */
 460                                 location->pc_location = PC_LOC_IN_LR;
 461                         } else if (bt_modifies_lr(&bundle)) {
 462                                 lr_modified = true;
 463                         }
 464                 }
 465         }
 466 }
 467
 468 void backtrace_init(BacktraceIterator *state,
 469                     BacktraceMemoryReader read_memory_func,
 470                     void *read_memory_func_extra,
 471                     VirtualAddress pc, VirtualAddress lr,
 472                     VirtualAddress sp, VirtualAddress r52)
 473 {
 474         CallerLocation location;
 475         VirtualAddress fp, initial_frame_caller_pc;
 476
 477         if (read_memory_func == NULL) {
 478                 read_memory_func = bt_read_memory;
 479         }
 480
 481         /* Find out where we are in the initial frame. */
 482         find_caller_pc_and_caller_sp(&location, pc,
 483                                      read_memory_func, read_memory_func_extra);
 484
 485         switch (location.sp_location) {
 486         case SP_LOC_UNKNOWN:
 487                 /* Give up. */
 488                 fp = -1;
 489                 break;
 490
 491         case SP_LOC_IN_R52:
 492                 fp = r52;
 493                 break;
 494
 495         case SP_LOC_OFFSET:
 496                 fp = sp + location.sp_offset;
 497                 break;
 498
 499         default:
 500                 /* Give up. */
 501                 fp = -1;
 502                 break;
 503         }
 504
 505         /* The frame pointer should theoretically be aligned mod 8. If
 506          * it's not even aligned mod 4 then something terrible happened
 507          * and we should mark it as invalid.
 508          */
 509         if (fp % 4 != 0)
 510                 fp = -1;
 511
 512         /* -1 means "don't know initial_frame_caller_pc". */
 513         initial_frame_caller_pc = -1;
 514
 515         switch (location.pc_location) {
 516         case PC_LOC_UNKNOWN:
 517                 /* Give up. */
 518                 fp = -1;
 519                 break;
 520
 521         case PC_LOC_IN_LR:
 522                 if (lr == 0 || lr % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
 523                         /* Give up. */
 524                         fp = -1;
 525                 } else {
 526                         initial_frame_caller_pc = lr;
 527                 }
 528                 break;
 529
 530         case PC_LOC_ON_STACK:
 531                 /* Leave initial_frame_caller_pc as -1,
 532                  * meaning check the stack.
 533                  */
 534                 break;
 535
 536         default:
 537                 /* Give up. */
 538                 fp = -1;
 539                 break;
 540         }
 541
 542         state->pc = pc;
 543         state->sp = sp;
 544         state->fp = fp;
 545         state->initial_frame_caller_pc = initial_frame_caller_pc;
 546         state->read_memory_func = read_memory_func;
 547         state->read_memory_func_extra = read_memory_func_extra;
 548 }
 549
 550 bool backtrace_next(BacktraceIterator *state)
 551 {
 552         VirtualAddress next_fp, next_pc, next_frame[2];
 553
 554         if (state->fp == -1) {
 555                 /* No parent frame. */
 556                 return false;
 557         }
 558
 559         /* Try to read the frame linkage data chaining to the next function. */
 560         if (!state->read_memory_func(&next_frame, state->fp, sizeof next_frame,
 561                                      state->read_memory_func_extra)) {
 562                 return false;
 563         }
 564
 565         next_fp = next_frame[1];
 566         if (next_fp % 4 != 0) {
 567                 /* Caller's frame pointer is suspect, so give up.
 568                  * Technically it should be aligned mod 8, but we will
 569                  * be forgiving here.
 570                  */
 571                 return false;
 572         }
 573
 574         if (state->initial_frame_caller_pc != -1) {
 575                 /* We must be in the initial stack frame and already know the
 576                  * caller PC.
 577                  */
 578                 next_pc = state->initial_frame_caller_pc;
 579
 580                 /* Force reading stack next time, in case we were in the
 581                  * initial frame.  We don't do this above just to paranoidly
 582                  * avoid changing the struct at all when we return false.
 583                  */
 584                 state->initial_frame_caller_pc = -1;
 585         } else {
 586                 /* Get the caller PC from the frame linkage area. */
 587                 next_pc = next_frame[0];
 588                 if (next_pc == 0 ||
 589                     next_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
 590                         /* The PC is suspect, so give up. */
 591                         return false;
 592                 }
 593         }
 594
 595         /* Update state to become the caller's stack frame. */
 596         state->pc = next_pc;
 597         state->sp = state->fp;
 598         state->fp = next_fp;
 599
 600         return true;
 601 }
 602
 603 #else /* TILE_CHIP < 10 */
 604
 605 void backtrace_init(BacktraceIterator *state,
 606                     BacktraceMemoryReader read_memory_func,
 607                     void *read_memory_func_extra,
 608                     VirtualAddress pc, VirtualAddress lr,
 609                     VirtualAddress sp, VirtualAddress r52)
 610 {
 611         state->pc = pc;
 612         state->sp = sp;
 613         state->fp = -1;
 614         state->initial_frame_caller_pc = -1;
 615         state->read_memory_func = read_memory_func;
 616         state->read_memory_func_extra = read_memory_func_extra;
 617 }
 618
 619 bool backtrace_next(BacktraceIterator *state) { return false; }
 620
 621 #endif /* TILE_CHIP < 10 */